Manufacture of articles from liquid dispersions



e 19, 1945 E.-E.HABI B Em 2 378,7

. MANUFACTURE OF ARTICLES FROM LIQUID DISPERSIONS Filed Nov. 16, i945layer of coagulont liquid conraininq acceleraror F|G 2 accelera'for'solud'lon surface wcf wrfh accelenflor scalmrion FlG.4

warm Clll EMILE E. HABIB GORDON E. GOTT Inventors By Pit ntod June 19,1945 2.37am I l I MANUFACTURE OF narrows msrunsrous moumqum Emile E.Habib' and Gordon ErGott, Arlington, Mass, assignors to Dewey and Almy(Chemical Company, North Cambridge, Mass, a oorpora= tion ofMassachusetts Application November is, ices, Serial No. amass (cl.ia-ss) 3 Elaims.

' The present invention relates to the manufacture of hollow rubberobjects and more particularly to the manufacture of large-sizemeteorological and radiosonde balloons by a coagulant dipping process.

Balloons of this recent past by a casting procedure. This was a slowprocess and save control difiiculties because of the sensitivity andlack of stability of the dispersion; These dimculties were avoided bythe introduction of a coagulant dipping process in which the depositedlayer of rubber is stripped from the dipping mold while it is stillplastic and is subsequently inflated to the desired larger size.

This processis described in detail in our copend- 1 ing applicationSerial No. 510,442, filed on the same day as the present application.

This improved dipping type process was found to be applicable to naturallatex dispersions only with the limitation that the dipping compound beused before the percentage of sulfur combined on the rubber hydrocarbonhad risen to more than 0.45%, based on the dry weight of thehydrocarbon. If a natural latex dispersion in which the combined sulfuron the rubber hydrocarbon exceeds 0.45% is used, the freshly depositedgels can not be stretched enough to get them Oh the mold without tearingthem. If they are allowed to drytype had been made until the and thusacquire'sufilcient strength for stripping,

then they can not be permanently enlarged enough by inflation becausethe material is no longer capable of sufilcient plastic flow. Thischaracteristic of the process means ping bath must'be freshly preparedand used when not more than a few days old. For laboratory scaleoperation, this characteristic is not a serious handicap, but thoseskilled in the art will appreciate immediately the difificulties itcauses when the Process is used on a factory scale.

It is the principal object of the present invention to overcome thedimculty described above; to provide a modification of the coagulantdipping process referred to above which will adapt it to efficient andeconomic factory scale operation; and to provide a means of preventingthe combined' sulfur of the dipping bath from rising to an undesirableamount before the bath is used.

We have discovered a satisfactory procedure .for introducing .asufficiently large amount of a vulcanization accelerator into the wetgels formed in the proces described in the application referred to abovewhich will distribute the accelerator uniformly inthe gel without localconcentrations which would produce non-uniform cure. This procedure isavailed of to accomplish the objects of the invention by. omitting that,the d p-- the dipping compound the accelerawr,

the compound for dipping in the normal manner, and then introducing anaccelerator into the formed objects. As a consequence of the absence ofan accelerator from the compound, modern hish=speed accelerators may beused with the process and the compounds do not materially change intheir combined sulfur content upon ageing and, therefore, need not befreshly prepared.

The invention will be more fully understood from a reference to theaccompanying drawing.

in which Figure 1 is an elevation partly in section of the dipping moldafter it has been'withdrawn from the dispersion withthe deposited gellayer on its "dispersion of natural latex and also make up a suitablecoagulant compound. The following example illustrates compoundswhioh'are suitable:

Parts by weight of solids Rubber latex (60% solids) 100.00 Potassiumhydroxide 1.75 Zinc. stearate 1.00

Symmetrical di-beta-naphthyl para phenylene diamine 1.00 Formaldehydecondensation product of naphthalene sulphonic acid 0.24

Titanium dimride 1.00

, Sulphur 1.10

ingredients are added in the order stated.

The amount will vary with different latices; suficieni: shouldbe used togive the dispersion a viscosity suitable for dipping.

The coagulant has the following composition:

Bentonite 150 Water 900 Acetone 1,321 Calcium nitrate tetra hydrate1,250 Glycerine Glacial acetic acid 37 A suitably shaped balloon mold lis dipped into the coagulant composition and then withdrawn,

forming on its surface a layer of coagulant l.

mold I together with the deposited gel layer B on: its surface is thenimmersed in ninth as shown in Figure 2 containing a suitable acceleratorof vulcanization. The accelerator may be in solution or in suspension.For gels formed from the composition of Example 1, a suitable bath maybe made by dissolving parts of potassium pentamethylene dithiocarbamatein 90 parts or water, and the mold should be held in the accelerator forabout minutes. The mold is then withdrawn from the accelerator and the.gel layer I is stripped from its surface by stretching the neck of thegel and sliding it downwardly oil the form as shown in Figure 3. The gellayer is then placed on an inflating nozzle and blown up to the desiredsize as shown in Figure 4. .During the inflation it is found that theliquid accelerator is caused by the stretching of the gel material to beabsorbed into the gel. The gel is then dried in inflat d condition asshown in Figure 4 and, when it has been dried, is deflated and heated indry air at 212 F. to bring about vulcanization as shown in Figure 5. Itis found that the vulcanization proceeds normallybecause of the presenceof the accelerator which has been drawn into the gel during inflation.

It is essential that the step'of soaking the gel article in theaccelerator be carried out before the article is inflated, because, inaddition to absorption of accelerator into the gel during soaking, thereis a relatively enormous absorption of accelerator into the gel as thegel is expanded during inflation. By inflating the latex from the mold,although we have found that the gels may be more conveniently handledand immersed while they are still on the molds.

It will be appreciated that the objects of the invention may be attainedby including in the dipping bath only a small amount of accelerator, theparticular amount depending upon plant conditions.

, The present invention, it will be appreciated, is equally applicableto the manufactureoi other objects than the meterological balloonsselected as the specific exam le for purposes of disclosure. The presentprocess may be used'in the manufacture of any rubber article which lendsitself to production by the process of our copending application, SerialNo. 510,442 (on which the present invention is an improvement).

-We claim:

1. The process of manufacturing rubber articles which comprises dippinga coagulant-coated mold into a. liquid dispersion of natural rubbercompounded for vulcanization except that it is deficient in accelerator,withdrawing the mold article while wet with an accelerator solution fromthe dispersion with a deposit of rubber gel thereon, soaking the gel ina liquid containing an accelerator of vulcanization, expanding the gelwhile it is still plastic and thereafter drying and vulcanizing the gel.

2. The process of manufacturing rubber articles which comprises dippinga coagulant-coated mold into a liquid dispersion of natural rubbercompounded for vulcanization except that it is deficient in accelerator,withdrawing the mold from the dispersion with a deposit of rubber gelthereon, immersing the'mold and gel in a liquid containing anaccelerator of vulcanization, stripping the gel from the mold, expandingthe gel while it is still plastic and thereafter drying and vulcanizingthe gel. n

3. The process of manufacturing rubber articles which comprises dippinga coagulant-coated mold into a liquid dispersion of natural rubbercompounded for vulcanization except that it is deficient in accelerator,withdrawing the mold from the dispersion with a deposit of rubber gelthereon, stripping the gel from the mold, soaking the gel in a liquidcontaining an accelerator of vulcanization, expanding the gel while itis still plastic, and thereafter drying and vulcanizing the gel.

Em E. HABB. GORDON E. GO'I'I'.

